1. Field of the Invention
This invention relates to an air suspension system, and more particularly to an air suspension system for a vehicle which can adjust a car height by changing the volume of an air spring.
2. Description of the Prior Art
An air suspension capable of adjusting the car height is provided with an air spring between a car body and a suspension arm. By changing the volume of compressed air in the air spring the car height can be adjusted to be high, normal or low for example. However, since the spring constant of the air spring is given as a function of the volume, the spring constant of the air spring automatically changes with every adjustment of the car height.
By changing the spring constant of the air spring, the following problems are presented.
For example, when an automobile travels on a bad road and the car height is increased, the spring constant is reduced so that so-called bottoming is caused so as to provide a worse ride. Also, a small spring constant produces fluttering so that contact of the wheel to the ground and thus controllability are degraded.
When the car height is reduced in high speed travelling, the spring constant is enlarged so as to result in a worse ride.
In an air suspension disclosed in the Japanese Patent Public Disclosure (KOKAI) No. 75813/84, a helper or a bound stopper disposed in an air spring is formed to be moved by a cylinder mounted in the air spring. Thus, the distance between the helper and the cylinder is maintained constant according to the signal of a helper position sensor. According to the air suspension, when the car height is increased to reduce the spring constant, bottoming out can be prevented and riding comfort can be improved.
However, no corrective measure is taken for the increase in the spring constant, and since the helper is moved by the cylinder disposed in the air spring, the volume of the air spring is changed by movement of the cylinder itself.